Method and device for transventricular mechanical circulatory support

ABSTRACT

Invention relates to a cannula and a screw pump for use in a mechanical circulatory support device, in particular a transventricular circulatory support device. The cannula according to the present invention comprises a tubular member made of a flexible, collapsible material having a diameter between 0.5 cm and 3 cm, preferably between 1 cm and 2.5 cm. The invention also relates to an inflatable screw pump for use in circulatory support system which comprises a flexible central drive shaft and an inflatable body having a free edge defining a spiral shaped contour around the central drive shaft and an inner edge connected to the drive shaft. The Archimedes type screw pump may be used in conjunction with the flexible cannula. The method of connecting the circulatory assist device to the heart comprises the steps of introducing the distal end of a cannula into a large systemic vein or into the right or left atrium, guiding the distal end of the cannula via the atrium to the inflow valve of the ventricle, and from there into the ventricle, guiding the distal end of the cannula from the ventricle to the ventricle outflow valve and from there into the pulmonary artery, the aorta or a side branch of the aorta and, connecting the proximal end of the cannula to a pump.

FIELD OF THE INVENTION

The invention relates to a cannula and a screw pump for use in amechanical circulatory support device in particular a transventricularcirculatory support device. The invention also relates to a method ofproviding mechanical transventricular support in open and closed chestapproaches using said cannula and/or said screw pump.

BACKGROUND OF THE INVENTION

In the course of coronary artery bypass grafting (CABG) without the useof the classical heart-lung machine, it may be required to provide amechanical circulatory support system to boost failing heartperformance. During bypass grafting on the beating heart, occlusion ofsegments of coronary arteries can cause failure of the pump function ofboth heart chambers due to lack of oxygen in the heart muscle or due toarrhytmia. Displacing of the beating heart within the thorax to obtainaccess to the coronary anastomotic site of the heart, may also lead tomechanical interference with the pump function. This may require thetemporary use of an auxiliary blood pump. Such a blood pump may beplaced outside or inside the blood circulation. The right and left heartchambers form two pumps placed in series, which may each be assisted intheir pump function by a right ventricle assist device (RVAD) and leftventricle assist device (LVAD), respectively.

For a right ventricle assist device (RVAD), the pump outside thecirculation bypasses the blood flow that enters the right atrium andthat passes from the right atrium via the right ventricle into thepulmonary trunc. Placement of the pump outside the circulation leads totwo holes in the circulatory system, one access hole for the cannulathat supplies blood from the venous side of the systemic circulation tothe assist pump and a second access hole for the output cannula of theassist pump. The inflow cannula of the assist pump may be put in placevia a stab wound in the right atrium or right ventricle wall, or via apuncture in a large systemic vein, such as the jugular or femoral vein.The outflow cannula of the assist pump can be placed distal to the rightventricular outflow valves e.g via a puncture hole in the pulmonarytrunc. For a LVAD, the bypass connects the left atrium or left ventricleto the aorta, or may comprise an apical cannulation.

Different types of extra-corporeally placed assist pumps may be used,such as a DeBakey roller pump, continuous flow pumps such as centrifugalpumps and rotary blood pumps, pulsatile pumps, etc.

When the assist pump is used within the circulation, only a singleaccess site is needed. An axial catheter-mounted screw pump, marketed byJohnson & Johnson of Warren, N.J. under the trade name HEMOPUMP,utilises a principle similar to that of an Archimedes screw. When usedfor left ventricle support, the screw element, which is placed inside acurved silicone rubber catheter, is positioned in the aorta, with theinlet in the left ventricle lumen. The pump assembly is made ofstainless steel and has about the size of a pencil. The drive motor ofthe screw element is located extracorporeally, and drives the screwelement at about 25000 rpm such that the pump draws a steady stream fromthe left ventricle. For right ventricle support, the pump can beinserted in the pulmonary artery through a stab wound, the inlet sidebeing positioned in the lumen of the right ventricle.

The above methods of cannulation for the intra and extracorporeallyplaced assist pumps have several disadvantages. Firstly, access to thecirculation is achieved through a cut in possibly calcified vessels.Secondly, the methods may result in dislodgement of plaque withconsequent risk of embolisation. Thirdly, false air aspiration may occurat the cannulation site for blood withdrawal, with subsequent risk ofair embolisation. Finally, in case a so-called “reverse hemopump” isused which is introduced into the circulation via one of the ventricles,or during cannulation of the apex of the left ventricle for a LVAD, acut into the heart muscle may lead to bleeding complications.

It is therefore an object of the present invention to provide a cannula,a pump, and method of using the same in right or left transventricularmechanical support, which avoid the above drawbacks, and which allow forrapid placement through the least vulnerable tissues without the need ofa cut in diseased blood vessels, such as a calcified ascending aorta orstenosed calcified peripheral arteries. It is a further object of thepresent invention to provide a cannula, pump and method oftransventricular mechanical circulatory support in which cannulation ofthe large outflow vessels of the right and left ventricle (pulmonarytrunc or artery and aorta, respectively) need not be cannulated, andwhich can be carried out in a minimally invasive manner, preferablyunder close chest conditions.

SUMMARY OF THE INVENTION

Hereto the cannula according to the present invention comprises atubular member made of a flexible, collapsible material having adiameter between 0.5 cm and 3 cm, preferably between 1 cm and 2.5 cm.Preferably the material of the cannula is substantially non-extendible.When used as a RVAD, the cannula according to the present invention canbe introduced into the right atrium via a cut into a larger vein,whereafter the distal end is introduced into the right ventricle via thetricuspid valve. The sharply curved trajectory at the apex of the rightventricle can be easily followed by the very flexible cannula of thepresent invention. From the right ventricle the flexible cannula isguided along the right ventricle outflow valve and is lodged with itsdistal (outflow) end in the pulmonary artery or pulmonary trunc. Theinflow side of the cannula may be connected to an extra orintracorporeally situated bloodpump. The very flexible cannula, whichupon insertion is collapsed to very small dimensions, may be inserteddirectly into the atrium during open or closed chest CABG or may beinserted in a peripheral vein (e.g. femoral or jugular or axillar vein)and advanced to a central location for blood delivery in the pulmonaryartery. The assist pump may remain outside the chest. A similarprocedure applies to the use of the cannula of the present invention forleft ventricle assist devices (LVAD). A LVAD may form a bypass fordrainage of blood from the left atrium and for blood delivery to theaorta. The flexible cannula may be introduced into the left atriumthrough the right upper pulmonary vein, or right atrium with subsequentperforation of the atrial septum, or via the left atrial roof or leftatrial appendage.

A suitable material for the cannula comprises polymer (polyethane)angioplastic balloon material or polyurethane with a wall thickness ofbetween 100 and 300 micrometer. Such material can easily drape and flexwithout being extendible, such that it can be collapsed to very smalldimensions to be easily manipulated within the heart.

In a preferred embodiment the cannula comprises a first lumen of arelatively large diameter and a second lumen parallel to the firstlumen, and of a smaller diameter. The second lumen may be formed bylengthwise sealing together opposite located walls of the flexiblecannula. A flexible guiding catheter may be introduced in the smallerlumen for guiding the flexible cannula to its proper position and forserving as a guideline that provides shape stability to the flexiblecannula in the axial direction. The end of the flexible cannula maycomprise a guide element of relatively short length such as a railrunner, for receiving a guide wire therethrough. The guide element maycomprise an internal thread such that the cannula may be transported byrotation of the threaded guide wire which propels the guide element.

In one embodiment, the flexible cannula comprises a balloon at or nearthe distal portion of the cannula which allows vacuum collapse of theproximal and mid portion of the cannula upon introduction. This preventsfilling of the lumen of the cannula and subsequently volume trapping.When the cannula is placed in its proper position, the guide catheterand the balloon may be withdrawn from the vessel or, alternatively, thecatheter may be left in place to serve as a backbone for providinglongitudinal dimensional stability to the flexible cannula. The secondlumen of the cannula surrounding the backbone catheter avoids stagnantflow areas and prevents direct blood contact with less biocompatiblecomponents of the catheter wire.

For attachment of the inflow side of the flexible cannula to a regularrigid cannula or to an intracorporeally located screw pump, the cannulamay at its proximal end comprise a ring-shaped inflatable element whichis provided with an inflation lumen. Upon inflation of the ring-shapedelement, the proximal end of the flexible cannula is clampingly engagedwith the rigid inflow cannula or with a screw pump attachment part.

Even though the flexible cannula according to the present invention maybe used with a pump which is placed either inside or outside the bloodcirculation, it is preferred that it is used together with an Archimedestype screw pump having a flexible central drive shaft and an inflatablebody having a free edge defining a spiral-shaped contour around thecentral drive shaft and an inner edge connected to the drive shaft. Theinflatable Archimedes type screw pump may be attached to the inlet sideof the cannula while its rotary drive shaft extends to outside the bodywhere it is rotated by a motor drive unit This yields a completelytransluminal ventricular assist system with an acceptable small diameterupon introduction and retrieval from a peripheral vessel and having asufficiently large diameter after expansion of the inflatable Archimedestype screw pump and the flexible cannula to deliver a blood flow at arate of 2 liters per minute or more.

For RVAD blood delivery to the pulmonary trunc the inflatable Archimedestype screw pump may be inserted through the peripheral access throughfemoral, jugular or axillar vein, or transthoracally through a key holeaccess directly into the right atrium. For LVAD, (blood delivery to theascending aorta), the right upper pulmonary vein, or the atrialappendage or the roof of the left atrium or the left ventricular apexmay be stabbed directly in the open chest or closed chest approach.Alternatively, for LVAD, access to the left heart side may be reachedfrom the venous circulation using the latter access and by subsequentlyperforating the wall (atrial septum) between the right and left atrium.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in detail with reference to theaccompanying drawings. In the drawings:

FIG. 1 shows a schematic cross-sectional view of the anatomy of theheart including a RVAD, and a LVAD,

FIG. 2 shows a RVAD using a flexible cannula according the presentinvention,

FIG. 3 shows the flexible cannula according to the present inventionincluding a backbone catheter,

FIGS. 4 shows a method of introducing the cannula according to thepresent invention along a guide rail,

FIG. 5 shows a ventricular assist device according to the presentinvention including an inflatable Archimedes type screw pump attached tothe proximal end of a flexible cannula,

FIG. 6 shows a cross-sectional view of the drive shaft of an inflatableArchimedes screw pump according to the present invention,

FIG. 7 shows an assembly of the flexible cannula having its proximal endattached to an inflatable Archimedes type screw pump according to thepresent invention,

FIG. 8 shows the intra ventricular course of the assembly of theArchimedes type screw pump and flexible cannula when used as a RVAD, and

FIG. 9 shows the attachment of the flexible cannula to the Archimedestype screw pump.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 a schematic representation of the basic anatomy of the heartis shown, showing parallel assisted pumping using a rightextracorporeally located ventricular assist device (RVAD) and a leftextracorporeally located ventricular assist device (LVAD). The arrowsindicate the direction of the blood flow. The RVAD comprises a pump 9which bypasses the blood circulation normally flowing from largesystemic veins (caval veins, CV) into the right atrium (RA), via theright ventricle inflow valve or tricuspid valve 6 into the rightventrical (RV). The bypass of the RVAD connects the caval veins (CV) orthe right atrium with the pulmonary trunc (PT) or with the pulmonaryartery. From the right ventricle the blood flow passes via the rightventricle outflow valve 7 into the pulmonary trunc and from there intothe lungs and from the lungs back into the left atrium (LA) via themitral valve 5 into the left ventrical (LV) and from thereon past theaortic valve 4 into the ascending aorta 3 and descending aorta 3″ (AO).

For the right ventricle assist pump 9, the inflow side 12 may beattached to a large systemic vein, the right atrium RA (appendix) or tothe right ventricle RV. The outflow side 11 of the RV assist pump 9 maybe attached to the pulmonary trunc PT.

The LV assist pump 10 ma have its inflow side 14 connected to the leftventricle LV or to the left atrium LA. The outflow side 13 of the LVassist pump 10 may be connected to the ascending aorta 3, to thedescending aorta 3″ or to a large side branch 3′. The pumping rates ofthe assist pumps 9,10 are up to 3 L/min or 10 L/min for partialventricular support (booster), depending on the requirements of thepatient.

FIG. 2 shows the intraventricular trajectory of the cannula according tothe present invention, in particular when used as a transventricularmechanical circulatory support system. The flexible cannula 15 extendsalong the sharply curved trajectory of the right ventricle RV and hasits outflow side located in the pulmonary trunc for blood delivery tothe lung circulation in combination with unloading the right ventricleRV. The cannula 15 is introduced to the venous circulation through a cutin the superior caval vein (CV), one of its side branches or in theright atrial tissue. Flexible cannula 15 is provided with a Swan-Ganzguiding catheter 18 which acts a backbone catheter and which its end isprovided with an inflatable balloon 19. When the outflow portion at thedistal end 17 of the cannula 15 has reached its position of optimalplacement in the pulmonary artery beyond the pulmonary valve, a rigidpreformed cannula 21 is inserted into the proximal end of the cannula15, which cannula 21 is connected to the outflow side of assist pump 20.The heart valves 6 and 7 fold over the easily collapsible material ofthe cannula 15. The collapsible cannula 15 is in its collapsed mode noobstruction to normal intracardiac flow when the assist pump 20 is riotactivated. The inflow side 22 of the pump 20 may be connected to asecond cannula which is not shown in the drawing and which may beinserted in the venous circulation.

FIG. 3 shows an assembly of the flexible cannula 23 according to thepresent invention which is provided with a “backbone” or guidingcatheter 27. The cannula 23 may have a length of between 15 and 30centimeters and has a diameter of between 0,5 and 3 centimeter,preferably about 2 centimeter. The flexible cannula 23 is made of a PTEpolymer material, angioplasty balloon material or polyurethane and has awall thickness of between 100 and 300 micrometers. The cannula 23comprises a lengthwise seal 24 along which the material of the walls ofthe cannula is fused. Thereby a first lumen 25 and a second lumen 26 areformed, which second lumen surrounds the guide catheter 27. The cannula23 may exist of an ultra thin wall, non-extendible, highly flexiblepolymer such as for instance used for waste or refuse collection bags.When deployed, the cannula 23 cannot distend further by elasticdeformation such that the positions of its proximal and distal ends areaccurately defined, and that no overdistention, or ballooning occurs,with consequent risk of obstruction of native blood flow. The balloontipped (balloon 29) backbone guiding catheter 27 is flexible and allowssteering, similar to a diagnostic Swan-Ganz catheter. At its distal end,the cannula 23 is provided with an internal balloon 28 which allowsvacuum collapse of the proximal and mid portion of the cannula 23 uponintroduction, which prevents filling of the lumen 25 and subsequentvolume trapping. The guide catheter 27 is provided with an additionalinflation lumen ending at the balloon 28. After the cannula 23 has beenintroduced into the circulation, the cannula 23 is unfolded byincreasing the pressure at the inlet by supplying blood or a salinesolution, so that it assumes its tubular shape. When the cannula is inits required position, the balloon 28 is deflated to open the outflowend of the cannula.

FIG. 4 shows an embodiment wherein the flexible cannula 30 is at itsdistal end provided with a rail runner 31 which is placed around theguide wire 32. The guide wire 32 may first be placed in the circulationalong the curved trajectory through the heart. Thereafter the railrunner 31 at the distal end of cannula 30 is placed over the guide wireand is thereafter pushed forward by a tube 33 which is placed over theguide wire 32. In this way the flexible cannula 30 is pushed forward andcan be finally positioned. In an alternative embodiment the rail runner31 may contain an internal screw thread and the guide wire 32 may beprovided with an external screw thread. By rotation of the guide wire32, the rail runner 31 can be moved ahead.

FIG. 5 shows an assembly comprising a flexible cannula 41 and locatedtherein an inflatable Archimedes type screw pump 40. The screw pump 40comprises a flexible central drive shaft 42, which is for instance madeof a flexible braiden metal wire. The screw pump 40 comprises a spirallywound inflatable tube 43 which is via a membrane 44 connected to thecentral drive shaft 42. Inflatable tube 43 is connected to a lower driveshaft 45 which is hollow and which comprises a central flexible driveshaft, a lubrication and cooling channel surrounding the central driveshaft and a separate saline inflation and deflation channel. The lowerdrive shaft 45 is rotatably connected to a motor unit 46 comprising alubrication and cooling port 48 and an inflation/deflation saline port47.

In the deflated state, the screw pump 40 will collapse and assume arelatively low profile which will allow insertion and retrieval througha relatively small puncture hole. The material of the membrane 44 andthe tubular body 43 may be Percutanous Transluminal Coronary Angioplasty(PTCA) balloon skin material which may withstand pressures of up to 30bar. Inflation of the tubular body 43 with saline to pressures up to 30bar will stretch the screw pump 40 longitudinally as well as radiallysuch that it assumes its Archimedean shape, with a diameter of the screwpump of between 0.5 and 3 cm, preferably about 2 cm. During rotation,the PTCA balloon skin material does not stretch. Due to its large walltension, the tubular body 43 will form a stiff structure suitable forpumping blood at rates of 2 liters per minute or more at relatively lowrotational speeds such as speeds of 1000 rpm. To create a forward flow,the inflated screw element formed by the inflatable tubular body 43 andthe membrane 44 may rotate within the stationary cylinder formed bycannula 41.

FIG. 6 shows a cross-sectional view of the lower part 45 of the driveshaft 42 wherein a central drive wire 49 which is surrounded by alubrication and cooling channel 50. A separate saline inflation channel51 is incorporated in the wall of the lower drive shaft 45.

FIG. 7 shows an integrated unit comprised of the flexible cannula 41into the proximal end of which an Archimedean screw pump 40 ispositioned. The rotary blood pump 40 may be electrically, pneumaticallyor externally cable driven such as shown in the figure, by the lowerpart 45 of the drive shaft 42 which is connected to an extracorporeallyplaced motor unit 46. In position, the length dimension of the flexiblecannula 41 is stabilised by backbone catheter 52.

FIG. 8 shows the transventricular application of an assembly consistingof the flexible cannula. 55 which contains in its proximal endArchimedes type screw pump 53. Then lower part 54 of the rotary driveshaft, as well as a backbone catheter 56 extend through the venoussystem to outside the patient's body. At its distal end, the cannula 55may be anchored into the pulmonary trunc PT by means of an inflatableanchoring mechanism 57, which allows unrestricted introduction of thecannula and an easy passage past the heart valves.

In the embodiment shown in FIG. 9, the flexible cannula 58 comprises atits proximal end an inflatable ring-shaped element 59 which will preventcollapse of the proximal end of the cannula upon suction created by therotation of the Archimedes type screw pump 60. The inflatable screw 60end the flexible cannula 58 may be introduced together through a two-wayintroducer with saline flush as its third port. The tip of the screw 60has to be lodged into the folded cannula 58 outside the vascular accesssite, but inside the introducer, which thereto is preferablytransparent.

In Vitro Experiment

The flexible cannula according to the present invention (length 40 cm,expanded diameter approximately 12 mm) was connected to a fluid pump.The device was coiled up twice and was torqued in the longitudinaldirection to mimic the pathway through a sharply bended trajectory.Water flow exceeded 7 L/min while the pressure gradient over the cannuladid not exceed 100 mm Hg. The cannula uncoiled, untwisted, unfolded andfully expanded spontaneously under pressurized water supply.

In Vivo Experiments

Five acute experiments in the living pig (80 kg) have been performed.Cannulation for the implementation of right heart bypass using theflexible cannula according to the present invention were tested in twodifferent access sites, i.e. central cannulation through the rightatrial appendage (n=1) and introduction through a peripheral vein (n=4).An extracorporeally located blood pump was used as right ventricularassist device and connected to the flexible cannula. The heart wasexposed by splitting the sternal bone. For blood withdrawal to the bloodpump, the venous circulation was cannulated in the classical fashion.

Central access. The introduction of the flexible cannula through theright atrial appendage and placement in the pulmonary artery wasaccomplished. Bypass flow exceeded 2 L/min.

Peripheral access. The right jugular vein was exposed and was puncturedfor the introduction of the flexible cannula. In all four cases cannulaplacement was accomplished successfully without adverse effects.Introduction time was eventually <5 minutes. Bypass flow exceeded 4L/minute while the right ventricle was visibly decompressed. Indisplaced beating heart, mechanical assistance of the right ventriclenormalized the systemic circulation. Control fluroscopy revealed atransit ventricular position of the cannula and deposition of contrastmedium in the pulmonary artery beyond the pulmonary valve without signsof valvular incompetence. Post-mortem examination showed that thecannula was situated correctly in the right ventricle ie passage throughthe tricuspid valve, the right ventricle lumen and the pulmonary valve.The tip was located in the pulmonary trunc. In no case trombosis wasnoted. In one additional case the cannula was introduced through theleft atrial appendage and placed in the left ventricle.

What is claimed is:
 1. Cannula for use in a circulatory support system comprising a tubular member made of a flexible, collapsible material having a proximal inflow opening and a distal open end and having a diameter between 0.5 cm and 3 cm, wherein the cannula is made of a substantially non-extendible plastic polymer sheet material and comprises a first lumen of a relatively large diameter and a second lumen parallel to the first lumen, the second Lumen having a smaller diameter for receiving a flexible guide wire element.
 2. Cannula (15, 23, 30, 41, 55, 58) according to claim 1, wherein the cannula has a wall thickness of between 50 and 500 micrometer, preferably between 100 and 300 micrometer.
 3. Cannula (23) according to claim 1, wherein at the boundary (24) between the first and second lumen, the opposite walls of the tubular member are connected along a sealing line that is offset from the center line of the tubular member.
 4. Cannula (30) according to claim 1, wherein the second lumen forms a guide element (31) at a distal end of the cannula, which is of a relatively short length compared to the length of the cannula, for receiving the guide wire element (32) therethrough.
 5. Cannula (30) according to claim 4, wherein the guide element (31) comprises an internal thread.
 6. Cannula (23) according to claim 1, comprising at or near a distal end an internal inflatable element (28), connected to the walls of the tubular member and connected to an inflation lumen, for collapsing a part of the cannula.
 7. Cannula (58) according to claim 1, the cannula being at its proximal end provided with a ring-shaped inflatable element (59) which is connected to the wall of the tubular member and which is coaxially located with respect to said tubular member, the inflatable element (59) being connected to an inflation lumen.
 8. Assembly comprising a cannula (23) according to claim 1, and a catheter (27, 56) extending through the second lumen (26), the catheter (27, 56) comprising at its distal end an inflatable element (29, 57).
 9. Assembly according to claim 8, wherein the inflatable element comprises an anchoring device (57) for anchoring the distal end of the cannula (23) in a blood vessel.
 10. Cannula according to claim 1, wherein the cannula has a diameter between 1 cm and 2.5 cm.
 11. Circulatory assist device comprising a cannula according to claim 1, and a screw pump element comprising: a flexible central drive shaft, a tubular inflatable body defining, when inflated, a spiral-shaped contour around the central drive shaft, and a membrane connecting the tubular body to the drive shaft, the membrane extending along the entire tubular body and spirally around the drive shaft, the screw pump element being located inside the cannula.
 12. Method of connecting a circulatory assist device to the heart, in particular a ventricular assist device, comprising the steps of: introducing the distal end of a cannula according to claim 1, into a blood vessel or into the left or right atrium; guiding the distal end of the cannula via the atrium to the inflow valve of the ventricle, and from there into the ventricle; guiding the distal end of the cannula from the ventricle to the ventricle outflow valve and from there into the pulmonary artery or the aorta; and connecting the proximal end of the cannula to a pump.
 13. Method according to claim 12, wherein a screw pump, having a flexible central drive shaft (42), and an inflatable body (43) having a free edge defining a spiral-shaped contour around the central drive shaft, and an inner edge connected to the drive shaft, is introduced together with the cannula or subsequent to placement of the cannula, in its deflated state, to be located inside the cannula at the proximal end thereof, the screw pump being thereafter inflated and rotated via the flexible drive shaft from an extracorporeally located drive motor.
 14. Screw pump element for use in a circulatory support system, comprising: a flexible central drive shaft, an inflatable tubular body defining, when inflated, a spiral-shaped contour around the central drive shaft, and a membrane connecting the tubular body to the drive shaft, the membrane extending along the entire tubular body and spirally around the drive shaft.
 15. Screw pump element according to claim 14, wherein the flexible drive shaft (45) at the proximal end of the inflatable body (43) comprises an inflation/deflation channel (51). 